// backend/performance.go
package main

import (
	"bytes"
	"context"
	"encoding/json"
	"io"
	"math"
	"net/http"
	"os"
	"runtime"
	"strconv"
	"strings"
	"sync/atomic"
	"time"

	gocpu "github.com/shirou/gopsutil/v3/cpu"
	godisk "github.com/shirou/gopsutil/v3/disk"
)

var serverStartedAt = time.Now()

var lastCPUUsageBits uint64 // atomic float64 bits

func setLastCPUUsage(v float64) { atomic.StoreUint64(&lastCPUUsageBits, math.Float64bits(v)) }
func getLastCPUUsage() float64  { return math.Float64frombits(atomic.LoadUint64(&lastCPUUsageBits)) }

func buildPerfSnapshot() map[string]any {
	var ms runtime.MemStats
	runtime.ReadMemStats(&ms)

	s := getSettings()
	recordDir, _ := resolvePathRelativeToApp(s.RecordDir)

	var diskFreeBytes uint64
	var diskTotalBytes uint64
	var diskUsedPercent float64
	diskPath := recordDir

	if recordDir != "" {
		if u, err := godisk.Usage(recordDir); err == nil && u != nil {
			diskFreeBytes = u.Free
			diskTotalBytes = u.Total
			diskUsedPercent = u.UsedPercent
		}
	}

	// ✅ Dynamische Disk-Schwellen (2× inFlight, Resume = +3GB)
	pauseGB, resumeGB, inFlight, pauseNeed, resumeNeed := computeDiskThresholds()

	resp := map[string]any{
		"ts":        time.Now().UTC().Format(time.RFC3339Nano),
		"serverMs":  time.Now().UTC().UnixMilli(), // ✅ für "Ping" im Frontend (Approx)
		"uptimeSec": time.Since(serverStartedAt).Seconds(),
		"cpuPercent": func() float64 {
			v := getLastCPUUsage()
			if math.IsNaN(v) || math.IsInf(v, 0) || v < 0 {
				return 0
			}
			if v == 0 {
				// Fallback: direkt messen, falls Controller nicht läuft / noch nicht gemessen hat
				if p, err := gocpu.Percent(0, false); err == nil && len(p) > 0 {
					return p[0]
				}
			}
			return v
		}(),
		"diskPath":        diskPath,
		"diskFreeBytes":   diskFreeBytes,
		"diskTotalBytes":  diskTotalBytes,
		"diskUsedPercent": diskUsedPercent,
		"diskEmergency":   atomic.LoadInt32(&diskEmergency) == 1,

		// ✅ statt LowDiskPauseBelowGB aus Settings
		"diskPauseBelowGB":  pauseGB,
		"diskResumeAboveGB": resumeGB,

		// ✅ optional, aber sehr hilfreich (Debug/UI)
		"diskInFlightBytes":   inFlight,
		"diskInFlightHuman":   formatBytesSI(u64ToI64(inFlight)),
		"diskPauseNeedBytes":  pauseNeed,
		"diskPauseNeedHuman":  formatBytesSI(u64ToI64(pauseNeed)),
		"diskResumeNeedBytes": resumeNeed,
		"diskResumeNeedHuman": formatBytesSI(u64ToI64(resumeNeed)),

		"goroutines": runtime.NumGoroutine(),
		"mem": map[string]any{
			"alloc":     ms.Alloc,
			"heapAlloc": ms.HeapAlloc,
			"heapInuse": ms.HeapInuse,
			"sys":       ms.Sys,
			"numGC":     ms.NumGC,
		},
	}

	sem := map[string]any{}
	if genSem != nil {
		sem["gen"] = map[string]any{"inUse": genSem.InUse(), "cap": genSem.Cap(), "max": genSem.Max()}
	}
	if previewSem != nil {
		sem["preview"] = map[string]any{"inUse": previewSem.InUse(), "cap": previewSem.Cap(), "max": previewSem.Max()}
	}
	if thumbSem != nil {
		sem["thumb"] = map[string]any{"inUse": thumbSem.InUse(), "cap": thumbSem.Cap(), "max": thumbSem.Max()}
	}
	if durSem != nil {
		sem["dur"] = map[string]any{"inUse": durSem.InUse(), "cap": durSem.Cap(), "max": durSem.Max()}
	}
	if len(sem) > 0 {
		resp["sem"] = sem
	}

	return resp
}

func pingHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodHead {
		http.Error(w, "Nur GET/HEAD erlaubt", http.StatusMethodNotAllowed)
		return
	}
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(http.StatusNoContent)
}

func perfHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "Nur GET erlaubt", http.StatusMethodNotAllowed)
		return
	}

	resp := buildPerfSnapshot()

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "no-store")
	_ = json.NewEncoder(w).Encode(resp)
}

func perfStreamHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "Nur GET erlaubt", http.StatusMethodNotAllowed)
		return
	}

	fl, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "Streaming nicht unterstützt", http.StatusInternalServerError)
		return
	}

	// Optional: client kann Intervall mitgeben: /api/stream?ms=5000
	ms := 5000
	if q := r.URL.Query().Get("ms"); q != "" {
		if v, err := strconv.Atoi(q); err == nil {
			// clamp: 1000..30000
			if v < 1000 {
				v = 1000
			}
			if v > 30000 {
				v = 30000
			}
			ms = v
		}
	}

	w.Header().Set("Content-Type", "text/event-stream; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Connection", "keep-alive")
	// hilfreich hinter nginx/proxies:
	w.Header().Set("X-Accel-Buffering", "no")

	ctx := r.Context()

	// sofort erstes Event schicken
	send := func() error {
		payload := buildPerfSnapshot()

		var buf bytes.Buffer
		if err := json.NewEncoder(&buf).Encode(payload); err != nil {
			return err
		}

		// event: perf
		_, _ = io.WriteString(w, "event: perf\n")
		_, _ = io.WriteString(w, "data: ")
		_, _ = w.Write(buf.Bytes())
		_, _ = io.WriteString(w, "\n")
		fl.Flush()
		return nil
	}

	// initial
	_ = send()

	t := time.NewTicker(time.Duration(ms) * time.Millisecond)
	hb := time.NewTicker(15 * time.Second) // heartbeat gegen Proxy timeouts
	defer t.Stop()
	defer hb.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-t.C:
			_ = send()
		case <-hb.C:
			// SSE Kommentar als Heartbeat
			_, _ = io.WriteString(w, ": keep-alive\n\n")
			fl.Flush()
		}
	}
}

func startAdaptiveSemController(ctx context.Context) {
	targetHi := 85.0
	targetLo := 65.0

	if v := strings.TrimSpace(os.Getenv("CPU_TARGET_HI")); v != "" {
		if f, err := strconv.ParseFloat(v, 64); err == nil {
			targetHi = f
		}
	}
	if v := strings.TrimSpace(os.Getenv("CPU_TARGET_LO")); v != "" {
		if f, err := strconv.ParseFloat(v, 64); err == nil {
			targetLo = f
		}
	}

	// Warmup (erste Messung kann 0 sein)
	_, _ = gocpu.Percent(200*time.Millisecond, false)

	t := time.NewTicker(2 * time.Second)
	go func() {
		defer t.Stop()

		for {
			select {
			case <-ctx.Done():
				return
			case <-t.C:
				p, err := gocpu.Percent(0, false)
				if err != nil || len(p) == 0 {
					continue
				}
				usage := p[0]
				setLastCPUUsage(usage)

				// Preview ist am teuersten → konservativ
				if usage > targetHi {
					previewSem.SetMax(previewSem.Max() - 1)
					genSem.SetMax(genSem.Max() - 1)
					thumbSem.SetMax(thumbSem.Max() - 1)
				} else if usage < targetLo {
					previewSem.SetMax(previewSem.Max() + 1)
					genSem.SetMax(genSem.Max() + 1)
					thumbSem.SetMax(thumbSem.Max() + 1)
				}
			}
		}
	}()
}